German Patent DE 10 2009 033 499 A1 discloses a braking system having a brake master cylinder, which has at least one brake master cylinder piston and to which wheel brake circuits are connected, an electrically controllable pressure provision device, an electronic control and regulating unit for actuating the electrically controllable pressure provision device so as to regulate the hydraulic pressure output by the latter, and a pedal decoupling unit, which is inserted ahead of the brake master cylinder and has a retaining piston, the first annular surface of which combines with the brake master cylinder piston to delimit a first hydraulic chamber, which can be supplied with the pressure output by the electrically controllable pressure provision device. Supplying pressure to the first hydraulic chamber causes a force to be exerted on the brake master cylinder piston in an actuating direction and on the retaining piston counter to the actuating direction. The electrically controllable pressure provision device can be designed as an electrohydraulic actuator consisting essentially of a hydraulic cylinder/piston arrangement and an electric motor, which drives the piston. In addition, a high-pressure accumulator is provided in the braking system, and this can be charged by the electrically controllable pressure provision device via a shutoff valve. In order to enhance the dynamics of the braking system during pressure buildup operations, especially highly dynamic braking operations, DE 10 2009 033 499 A1 makes provision for the shutoff valve of the high-pressure accumulator to be switched to the open operating position thereof simultaneously with the activation of the electrically controllable pressure provision device, ensuring that the first hydraulic chamber is supplied with the pressure medium under high pressure in the high-pressure accumulator in addition to the volume of pressure medium made available by the pressure provision device. This operation results in a rapid pressure buildup in the first chamber and hence in the brake master cylinder and the wheel brakes. In the method, described in DE 10 2009 033 499 A1, of connecting the high-pressure accumulator, the shutoff valve is therefore opened simultaneously with the activation of the pressure provision device, and the first hydraulic chamber is supplied with pressure medium simultaneously by the pressure provision device and the high-pressure accumulator.
In order to achieve a pressure buildup time which is as short as possible, the accumulator volume of the high-pressure accumulator should be as large as possible since the achievable pressure buildup time depends on the accumulator volume, more specifically the minimum achievable pressure buildup time increases as the accumulator volume grows smaller. Owing to the production costs and the limited installation space available for the high-pressure accumulator, however, it is often desirable that the selected accumulator volume of the high-pressure accumulator should be as small as possible.
It is therefore the underlying object of the present invention to provide a method for operating a braking system by means of which a sufficiently rapid pressure buildup can be achieved, even when using a high-pressure accumulator with a small accumulator volume.